Using untreated wood to make outdoor furniture?

I need advice from you woodworking pros.
We bought one of those kits, where all you do is add the 2x4s to make a 6-foot wide outdoor bench that converts to half a picnic table. Because the bench would be outside all year round, I originally put it together using treated 2x4s. Not being an experienced woodworker, I didn't realize that once the treated wood dried out, the treated 2x4s would end up all twisted and warped because the supports on this bench are about 5 feet apart, so the boards span about 5 feet.
Now we're going to replace the treated 2x4s with untreated 2x4s. I was considering buying cedar 2x4s, which we would varnish or polyurethane so the cedar doesn't turn gray. However, cedar is pretty expensive, and someone told me that as long as you're going to varnish or polyurethane the wood, you might as well save money and use regular, untreated pine 2x4s. He said, as long as you varnish or polyurethant the wood once a year, it shouldn't rot from being outside. (BTW, the wood does not contact the ground on this bench.)
I know that, theoretically, that should be the case. But will the bench really last as long as if I used cedar? Has anyone built outdoor furniture from pine ... and if so, how long does it last? If pine will work fine, I'd prefer that because cedar costs, what, 3X more?
Any advice would be appreciated!! Also, are there any tricks to working with treated wood, so it doesn't twist and warp when it dries out? From my experience, it seems treated boards are only suitable when you're screwing it down every 16 inches or so, like on a deck. But maybe there are tricks I don't know of.
--
NOTE: Please delete the word "REMOVE" from my e-mail address when replying.
This is a spam guard.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You should be OK with out the cedar or PT. One hint, don't use regular polyurethane, it does not take UV light very well. Get marine polyurethane.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Insects will not infest cedar but they will infest pine. If it were me I would use mahogany with 2 coats of "Penofin".
treated lumber I definitely would not use (those slivers are awful) not to mention the twisting and cracking after is dries out.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snip>

Couple things. First, PT is a total waste, IMHO. Would should not have its "feet wet" and should have some protective coating. Pine 2x4s? I don't think so. Likely choices are douglas-fir and spruce. The former is stronger but more brittle, and less tolerant of outdoor exposure. I'd go for good quality spruce, with a coat of paint or pigmented stain. Works for me.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.